1. Field of the Invention
This invention relates to an injection molding machine comprising an injecting unit defining a horizontal injection axis and comprising a plasticizing cylinder centered on and movable along the injection axis; the injecting unit is mounted to be movable in a horizontal shifting direction transversely to the injection axis to a plurality of injecting positions and adapted in these injecting positions to selectively discharge plastic material out of the plasticizing cylinder along the injection axis on a plurality of parallel paths into central gatings of first injection molds and off-center gatings of further injection molds, whereby a stationary mold carrier is provided with an enlarged opening in shifting direction for receiving the plasticizing cylinder, which is moved by at least one drive unit along the injection axis into and out of engagement with any of the injection molds, when one of them is mounted on the mold carrier for the injection of synthetic material into mentioned gating. The stationary mold carrier is adapted to selectively carry the first and further injection molds. Guiding elements for ending sections of the drive unit extend up to the stationary mold carrier and are guided in shifting direction when displacing the injection molding unit, whereby free ends of the ending sections are received in seats of at least one seat support displaceable on guiding means; the seat support comprises space for horizontal movement of the plasticizing cylinder onto the gating.
2. Description of the Prior Art
An injection molding machine of this kind is known from German Patent 40 34 577. This machine is adapted to selectively use further injection molds having off-center gatings in different injecting positions defining a central mold cavity. Under these conditions the plasticized synthetic material once injected reaches the mold cavity via a gate running approximately parallel with respect to the closing direction of the mold closing unit. Mentioned gate ends at the border of the mold cavity. A gate system of such a kind in the following is called "parallel gating". In this machine the piston rods lying in a horizontal plane are movably guided in a bushing support, which is passively carried along when the injection molding unit is shifted or also can be displaced manually. When the synthetic material is injected, a force in the piston rods opposed to the bearing pressure of the plasticizing cylinder effects that the bushing support is locked at punctiform guiding elements. Certainly it is a simple way to solve the connection of the bushings receiving the piston rods from the bushing support to the mold carrier, however, a field of force in the mold carrier results from the distance between the straining point of the piston rods and the force introducing points of the guiding elements, which makes necessary a lateral displacement of said guiding elements if shiftings of a large extent are realized. Consequently this facility is not adapted for an automatized shifting over the whole breadth of the mold carrier.
U.S. Pat. No. 5,007,816 discloses a unit of this kind in which the injection molding unit is bedded on a carrier made of cast iron, which bears the injection molding unit and is shiftable on horizontal guidings to central and off-centered gatings. The shifting movement is realized by a shifting device operateable by program, which comprises a distance measuring system as well as a spindle driving. The shifting device is detachably fixed at the carrier. This arrangement allows a precise support and adjustment of the injection molding unit, whereby it is consciously accepted that costly supporting measures, in this case a shifting table, have to be provided. A further problem in this connection is that the feed screw is not easily accessible, especially for cleaning purposes, due to the preset arrangement of the injection molding unit parallely with respect to the injection axis.